Insulation failure inspecting apparatus, insulation failure inspecting method using same, and method for manufacturing electrochemical cell

ABSTRACT

Disclosed is a method for manufacturing an electrochemical cell, wherein an insulation failure product can be accurately rejected, and an electrochemical cell can be used again after the insulation failure inspection. In the method for manufacturing the electrochemical cell ( 1 ), which is configured by hermetically housing an electrochemical cell main body ( 20 ) such that the leading end of a metal terminal ( 21 ) protrudes to the outside of the outer housing ( 10 ), an impulse voltage is applied between the metal terminal ( 21 ) and a metal foil layer ( 12 ), the waveform of the voltage applied to the capacitance between the metal terminal ( 21 ) and the metal foil layer ( 12 ) is measured, and the insulation failure inspection step is performed.

TECHNICAL FIELD

The present invention generally relates to an insulation failureinspecting apparatus, an insulation failure inspecting method using thesame, and a method for manufacturing an electrochemical cell, andparticularly relates to a method for manufacturing an electrochemicalcell, which allows a defective product having an insulation failure tobe rejected accurately and an electrochemical cell that has undergone aninsulation failure inspection to be reused.

BACKGROUND ART

A lithium ion battery is referred to also as a lithium secondarybattery, and examples thereof include a lithium ion battery that has aliquid-, gel-, or high polymer-type electrolyte and uses high polymersas positive electrode and negative electrode active materials. A lithiumion battery has a configuration including a positive electrode currentcollecting material, a positive electrode active material layer, anelectrolyte layer, a negative electrode active material layer, anegative electrode current collecting material, and an outer packagingbody that packages these materials and layers, and a multilayer film isused as a packaging material for forming the outer packaging body.

FIG. 10 is a perspective view of a conventional lithium ion battery, andFIG. 11 is a sectional view of the lithium ion battery taken on lineA-A′ in FIG. 10. As shown in FIGS. 10 and 11, a lithium ion battery 101is configured by hermetically housing a lithium ion battery main body120 in an outer packaging body 110 constituted at least of a base layer111, a metal foil layer 112, and a heat-sealable resin layer 113.

The lithium ion battery main body 120 is constituted of a cell(electricity storage portion) including a positive electrode composed ofa positive electrode active material and a positive electrode currentcollector, a negative electrode composed of a negative electrode activematerial and a negative electrode current collector, and an electrolytefilled between the positive electrode and the negative electrode (noneof these is shown in the figures), and a metal terminal 121 that isconnected to each of the positive electrode and the negative electrodein the cell and whose tip end protrudes to the outside of the outerpackaging body 110.

In the manufacturing process of the lithium ion battery 101, however,there has been the following problem. That is, when the mutually opposedheat-sealable resin layers 113 of the outer packaging body 110 areoverlaid on each other, and a peripheral edge portion thereof isheat-sealed so that the lithium ion battery main body 120 ishermetically housed therein, the heat-sealable resin layer 113 might bethinned, due to heat and pressure applied thereto at the time of theheat-sealing, to such an extent that a short circuit occurs between themetal terminal 121 and the metal foil layer 112. Furthermore, after theheat-sealing, if the outer packaging body 110 is bent, a crack mightoccur in the heat-sealable resin layer 113, through which theelectrolyte filled in the outer packaging body 110 permeates from partof the heat-sealable resin layer 113 into the metal foil layer 112,leading to a short circuit, or, even if a short circuit has not yetoccurred between the metal terminal 121 and the metal foil layer 112, aminute crack might occur in the heat-sealable resin layer 113, whichwill possibly lead to a short circuit in the future.

Conventionally, as a solution to this problem, from among completedlithium ion batteries, samples for inspection are drawn at apredetermined frequency, with respect to each of which a predeterminedhigh voltage is applied between the metal terminal 121 and the metalfoil layer 112, and among the samples of the lithium ion battery 101,those in which, as a result of the voltage application, an insulationbreakdown has occurred in the heat-sealable resin layer 113 are allremoved from the production line as defective products having cracksthat might lead to a short circuit. This inspecting method, however, hasbeen disadvantageous in that the inspection can be performed only withrespect to lithium ion batteries drawn as samples, and in that, due tolow accuracy of the inspection, such a minute crack that it would notlead to a short circuit can hardly be identified. This inspecting methodhas been disadvantageous also in that, as a result of applying a highvoltage, it is highly likely that some samples of the lithium ionbattery 101 that are in fact not defective products have newly sufferedfrom an insulation breakdown and thus cannot be reused after theinspection.

Furthermore, Patent Document 1 describes a method in which plating isperformed to deposit metal on a metal foil layer constituting an outerpackaging body, and an insulation-deteriorated area is determined bychecking, by visual observation or the like, whether or not a metaldeposit is formed thereby. This inspection method described in PatentDocument 1, however, requires that a lithium ion battery be soaked in aplating bath and thus has been disadvantageous in that a lithium ionbattery that has undergone the inspection cannot be reused irrespectiveof a result of the inspection.

LIST OF CITATIONS Patent Literature

-   Patent Document 1: JP-A-2007-257974

SUMMARY OF THE INVENTION Technical Problem

In view of the above-described problem, it is an object of the presentinvention to provide an insulation failure inspecting apparatus, aninsulation failure inspecting method using the same, and a method formanufacturing an electrochemical cell, which allow a defective producthaving an insulation failure to be rejected accurately, and,particularly, a method for manufacturing an electrochemical cell, whichallows an electrochemical cell that has undergone an insulation failureinspection to be reused.

Solution to the Problem

In order to achieve the above-described object, the present inventionprovides a method for manufacturing an electrochemical cell in which anelectrochemical cell main body including a positive electrode composedof a positive electrode active material and a positive electrode currentcollector, a negative electrode composed of a negative electrode activematerial and a negative electrode current collector, and an electrolytefilled between the positive electrode and the negative electrode ishermetically housed in an outer packaging body formed by sequentiallylaminating at least a metal foil layer and a heat-sealable resin layerso that a tip end of a metal terminal that is connected to each of thepositive electrode and the negative electrode protrudes to an outside.The method includes an insulation failure inspecting step in which animpulse voltage is applied between the metal terminal and the metal foillayer, and a waveform of a voltage applied to a capacitance between themetal terminal and the metal foil layer is measured.

According to this configuration, utilizing the fact that there is apredetermined capacitance between the metal terminal and the metal foillayer, and if there is an insulation failure between the metal terminaland the metal foil layer, the capacitance between the metal terminal andthe metal foil layer decreases considerably, an insulation failurebetween the metal terminal and the metal foil layer can be detected byapplying a voltage between the metal terminal and the metal foil layerand by subsequently measuring a waveform of the voltage applied to thecapacitance between the metal terminal and the metal foil layer.Furthermore, since a voltage is applied as an impulse voltage, it is notrequired that the voltage application between the metal terminal and themetal foil layer be performed for a long time, and thus a phenomenon canbe prevented in which the heat-sealable resin layer partially melts,which leads to an insulation breakdown and thus to new occurrence of ashort circuit. Furthermore, by measuring a voltage waveform, theoccurrence of a crack that will possibly lead to a short circuit in thefuture can be detected based on a slight variation in the voltagewaveform. Thus, the accuracy of an insulation failure inspection can beincreased, and a breakdown of an electrochemical cell in the insulationfailure inspecting step can be avoided.

Furthermore, according to the present invention, in the above-describedmethod for manufacturing an electrochemical cell, the insulation failureinspecting step is performed after the metal terminal is held in asandwiched manner by the outer packaging body and a holding portionwhere the metal terminal is held is heat-sealed and before theelectrolyte is filled in the outer packaging body.

According to this configuration, even though, in the manufacturingprocess of an electrochemical cell, when the metal terminal is held in asandwiched manner by the outer packaging body and a holding portionwhere the metal terminal is held is heat-sealed, the heat-sealable resinlayer might be thinned, due to heat and pressure applied thereto by theheat-sealing, to such an extent that a short circuit occurs between themetal terminal and the metal foil layer, such a short circuit and acrack in the vicinity of the metal terminal can be detected by theabove-described insulation failure inspecting step.

Furthermore, according to the present invention, in the above-describedmethod for manufacturing an electrochemical cell, the insulation failureinspecting step is performed after the electrolyte is filled in theouter packaging body.

According to this configuration, a short circuit and a crack that mightoccur in a peripheral edge portion of the outer packaging bodyheat-sealed after the electrolyte is filled in the outer packaging bodycan be detected by the above-described insulation failure inspectingstep.

Furthermore, according to the present invention, in the above-describedmethod for manufacturing an electrochemical cell, the insulation failureinspecting step is performed by measuring a value of a hold voltage heldby the capacitance between the metal terminal and the metal foil layerimmediately after the voltage application is halted and a value of thehold voltage held by the capacitance between the metal terminal and themetal foil layer after a lapse of a predetermined time from the halt ofthe voltage application.

According to this configuration, immediately after the application of animpulse voltage, electric charge is charged up in the capacitancebetween the metal terminal and the metal foil layer, and a hold voltageheld by this capacitance thus reaches a maximum value. If there is aninsulation failure between the metal terminal and the metal foil layer,however, the voltage does not rise to a value in the vicinity of adesired maximum value. Furthermore, if there is no insulation failure, avoltage applied to the capacitance between the metal terminal and themetal foil layer decreases slowly, whereas if there is an insulationfailure, electric charge cannot be held, and thus the voltage decreasesabruptly. Thus, by measuring a value of a hold voltage immediately aftervoltage application is halted and a value of the hold voltage after alapse of a predetermined time from immediately after the halt of thevoltage application, an insulation failure can be detected accurately.

Furthermore, according to the present invention, in the above-describedmethod for manufacturing an electrochemical cell, a voltage of 10 V orlower is used as a voltage to be applied between the metal terminal andthe metal foil layer.

According to this configuration, even though the metal terminalconnected to the electrochemical cell main body hermetically housed inthe outer packaging body is insulated from the metal foil layer of theouter packaging body by the heat-sealable resin layer that is aninnermost layer of the outer packaging body, and applying a high voltagebetween the metal terminal and the metal foil layer might cause theheat-sealable resin layer to melt to bring the electrolyte filled in theouter packaging body into conduction with the metal foil layer, leadingto the occurrence of an insulation breakdown, by using a voltage of 10 Vor lower as an impulse voltage to be applied in the insulation failureinspecting step, new occurrence of an insulation breakdown can beprevented.

Furthermore, according to the present invention, in the above-describedmethod for manufacturing an electrochemical cell, in a heat-sealing stepin which a peripheral edge portion of the outer packaging body isheat-sealed so that the mutually opposed heat-sealable resin layers arebonded to each other, a margin region not to be heat-sealed is leftunsealed on an outer peripheral side relative to a heat-sealing region,and in the insulation failure inspecting step, an impulse voltage isapplied between a portion of the metal foil layer lying in the marginregion and the metal terminal.

According to this configuration, the margin region is formed on theouter peripheral side relative to the heat-sealing region, and aconnection terminal is connected to a portion of the metal foil layerlying in the margin region, and thus even if a flaw is generated on thesurface of the outer packaging body in an area lying in the marginregion, such a flaw on the surface of the outer packaging body can beremoved by cutting away the margin region after the insulation failureinspecting step.

Furthermore, the present invention also provides an insulation failureinspecting apparatus including: a voltage generation unit that appliesan impulse voltage to a subject of measurement; and a voltagemeasurement unit that measures a variation with time of a voltage heldby the subject of measurement.

According to this configuration, by measuring a variation in voltageheld by a subject of measurement after the application of an impulsevoltage to the subject of measurement, it can be detected accuratelywhether or not the subject of measurement has an insulation failure.

Furthermore, according to the present invention, in the insulationfailure inspecting apparatus configured as above, the voltage generationunit applies a voltage of 10 V or lower.

According to this configuration, by using a voltage of 10 V or lower asan voltage to be applied, it is possible to prevent melting of theheat-sealable resin layer and thus to prevent an insulation failure fromoccurring in an electrochemical cell in an insulation failure inspectingstep.

Furthermore, according to the present invention, in the insulationfailure inspecting apparatus configured as above, a connection terminalthat connects the insulation failure inspecting apparatus to a subjectof measurement has a holding portion for holding the subject ofmeasurement in a sandwiching manner, and the holding portion has asharp-shaped portion that bites into the subject of measurement througha base layer formed on a surface of the subject of measurement.

According to this configuration, by holding, in a sandwiching manner, anouter packaging body having the base layer as its outermost layer withthe holding portion, the sharp-shaped portion is made to bite into ametal foil layer through the base layer, and thus a voltage can beapplied easily from the connection terminal to the metal foil layer.

Furthermore, the present invention also provides an insulation failureinspecting method using the insulation failure inspecting apparatusconfigured as above. In the insulation failure inspecting method, withrespect to an electrochemical cell in which an electrochemical cell mainbody including a positive electrode composed of a positive electrodeactive material and a positive electrode current collector, a negativeelectrode composed of a negative electrode active material and anegative electrode current collector, and an electrolyte filled betweenthe positive electrode and the negative electrode is hermetically housedin an outer packaging body formed by sequentially laminating at least ametal foil layer and a heat-sealable resin layer so that a tip end of ametal terminal that is connected to each of the positive electrode andthe negative electrode protrudes to an outside, an impulse voltage isapplied between the metal terminal and the metal foil layer, and a valueof a hold voltage held by a capacitance between the metal terminal andthe metal foil layer immediately after the voltage application is haltedand a value of the hold voltage held by the capacitance between themetal terminal and the metal foil layer after a lapse of a predeterminedtime from the halt of the voltage application are measured.

According to this configuration, it is possible to provide an insulationfailure inspecting method that allows an electrochemical cell as asubject of measurement that has undergone an inspection to be reusedwhile preventing new occurrence of an insulation failure in theelectrochemical cell, which is attributable to the application of animpulse voltage.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a plan view schematically showing a step of a manufacturingprocess of a lithium ion battery of the present invention.

FIG. 1B is a plan view schematically showing a step of the manufacturingprocess of a lithium ion battery of the present invention.

FIG. 1C is a plan view schematically showing a step of the manufacturingprocess of a lithium ion battery of the present invention.

FIG. 1D is a plan view schematically showing a step of the manufacturingprocess of a lithium ion battery of the present invention.

FIG. 2 is a perspective view of a lithium ion battery according to thepresent invention.

FIG. 3 is a sectional view of the lithium ion battery taken on line B-B′in FIG. 2.

FIG. 4 is a diagram schematically showing a configuration of aninsulation failure inspecting apparatus used in an insulation failureinspecting step of the present invention.

FIG. 5 is a diagram for explaining an operation of the insulationfailure inspecting apparatus.

FIG. 6 is a diagram showing one example of voltage waveforms measured inthe insulation failure inspecting step.

FIG. 7A is a plan view schematically showing a step of a manufacturingprocess of a lithium ion battery of the present invention.

FIG. 7B is a plan view schematically showing a step of the manufacturingprocess of a lithium ion battery of the present invention.

FIG. 7C is a plan view schematically showing a step of the manufacturingprocess of a lithium ion battery of the present invention.

FIG. 7D is a plan view schematically showing a step of the manufacturingprocess of a lithium ion battery of the present invention.

FIG. 8 is a sectional view of a lithium ion battery in an insulationfailure inspecting step shown in FIG. 7C.

FIG. 9 is a plan view schematically showing a modification example ofthe manufacturing process of a lithium ion battery of the presentinvention.

FIG. 10 is a perspective view of a conventional lithium ion battery.

FIG. 11 is a sectional view of the lithium ion battery taken on lineA-A′ in FIG. 10.

DESCRIPTION OF EMBODIMENTS

The present invention provides a method for manufacturing anelectrochemical cell, which allows a defective electrochemical cellhaving an insulation failure to be rejected and an electrochemical cellthat has undergone an insulation failure inspection to be reused. Withreference to the appended drawings and so on, the following describes ingreater detail one embodiment of the method for manufacturing anelectrochemical cell of the present invention. In the following,however, descriptions of components common to those in FIGS. 10 and 11showing the conventional example are omitted.

FIGS. 1A to ID are plan views schematically showing a manufacturingprocess of a lithium ion battery of this embodiment, FIG. 2 is aperspective view of a lithium ion battery, and FIG. 3 is a sectionalview of the lithium ion battery taken on line B-B′ in FIG. 2. A lithiumion battery 1 represents one example of the “electrochemical cell” ofthe present invention. In the manufacturing process of the lithium ionbattery 1 of this embodiment, first, as shown in FIG. 1A, a packagingmaterial cut out from a film is press-molded to form an outer packagingbody 10 in which a housing space 10 a for housing a lithium ion batterymain body 20 is secured. Next, as shown in FIG. 1B, the outer packagingbody 10 is folded in two and closed in that state, with the lithium ionbattery main body 20 housed in the housing space 10 a. At this time, asshown in FIG. 1C, a metal terminal 21 is held in a sandwiched manner bythe folded outer packaging body 10 so that it protrudes to the outside,and a metal terminal holding portion 10 b is heat-sealed. Then, by aninsulation failure inspecting apparatus 30, an impulse voltage isapplied between the metal terminal 21 (negative electrode) and a metalfoil layer 12 constituting the outer packaging body 10 (a portion of themetal foil layer 12 lying over a region of the metal terminal holdingportion 10 b in which the metal terminal 21 is held in a sandwichedmanner), and a waveform of the applied voltage is measured by theinsulation failure inspecting apparatus 30, which is how a firstinsulation failure inspection in the metal terminal holding portion 10 bis performed. Next, as shown in FIG. 1D, an electrolyte is filled in theouter packaging body 10, and all sides of the outer packaging body 10 inthe folded state other than the metal terminal holding portion 10 b areheat-sealed so that the lithium ion battery main body 20 is hermeticallysealed in the outer packaging body 10, and thus the lithium ion battery1 is completed. Then, lastly, by the insulation failure inspectingapparatus 30, an impulse voltage is applied between the metal terminal21 (negative electrode) and the metal foil layer 12, and a waveform ofthe applied voltage is measured by the insulation failure inspectingapparatus 30, which is how a second insulation failure inspection isperformed.

In this case, in the first insulation failure inspecting step, theelectrolyte has not yet been filled between the metal terminal 21 andthe metal foil layer 12, and a capacitance between the metal terminal 21and the metal foil layer 12, therefore, is small. Based on this, it ispreferable to use a high voltage as an impulse voltage to be applied inthe first insulation failure inspecting step, and to be more specific,an insulation failure can be detected by applying a voltage of about1000 V for 90 milliseconds. Since a voltage is applied as an impulsevoltage, it is not required that the voltage application between themetal terminal 21 and the metal foil layer 12 be performed for a longtime. This can prevent a phenomenon in which a heat-sealable resin layer13 partially melts, which leads to an insulation breakdown and thus tonew occurrence of a short circuit. Furthermore, in the second insulationfailure inspecting step, the electrolyte has been filled between themetal terminal 21 and the metal foil layer 12, and a capacitance betweenthe metal terminal 21 and the metal foil layer 12, therefore, is large.Based on this, it is possible to use a low voltage as an impulse voltageto be applied in the second insulation failure inspecting step, and tobe more specific, an insulation failure can be detected by applying avoltage of about 10 V for 90 milliseconds. At this time, a waveform ofthe voltage applied to the capacitance between the metal terminal 21 andthe metal foil layer 12 is measured, and thus an insulation failure canbe detected based on a slight variation in the voltage waveform. Thisallows an insulation failure inspection to be performed by using a lowimpulse voltage and thus can avoid a breakdown of the electrochemicalcell 1 in an insulation failure inspecting step.

Next, the following describes in greater detail the first and secondinsulation failure inspecting steps. FIG. 4 is a diagram schematicallyshowing a configuration of an insulation failure inspecting apparatusused in an insulation failure inspecting step, FIG. 5 is a diagram forexplaining an operation of the insulation failure inspecting apparatus,and FIG. 6 is a diagram showing one example of voltage waveformsmeasured in the insulation failure inspecting step. The insulationfailure inspecting apparatus 30 includes a voltage generation unit 31and a voltage measurement unit 32 that can measure a waveform of avoltage applied to a capacitance of a subject of measurement.Furthermore, the lithium ion battery 1 as the subject of measurement hasa capacitance C between the metal terminal 21 and the metal foil layer12. By this configuration, at STEP 1 (T0 to T1), when an impulse voltageis applied between the metal terminal 21 and the metal foil layer 12from the voltage generation unit 31, electric charge is charged in thecapacitance C, so that a voltage rises in a predetermined waveform. Thisvoltage waveform is observed in the voltage measurement unit 32.Subsequently, at STEP 2 (T1 to T2), after the voltage application ishalted, the voltage charged in the capacitance C drops gradually, and atSTEP 3 (T2 to T3), is completely discharged via a resistance R. Assumingthat a waveform obtained in this case is referred to as an OK waveform,compared therewith, in a case where a short circuit has occurred betweenthe metal terminal 21 and the metal foil layer 12, at STEP 1, a voltagedrops abruptly without rising in a predetermined waveform (NG waveform1). Furthermore, in a case where an insulation breakdown has occurredafter the application of an impulse voltage, at STEP 2, a voltage dropsabruptly (NG waveform 2).

As discussed above, in the insulation failure inspecting step of thisembodiment, by using a capacitance provided between the metal terminal21 and the metal foil layer 12, a variation in waveform of a voltageapplied to the capacitance is observed, and thus not only a case wherethe lithium ion battery 1 has already suffered from a short circuit inthe manufacturing process but also a case where the lithium ion battery1 has a crack that will possibly lead to a short circuit in the futurecan be detected accurately.

Next, the following describes the insulation failure inspectingapparatus 30. The insulation failure inspecting apparatus 30 has thevoltage generation unit 31 and the voltage measurement unit 32. In thevoltage generation unit 31, an impulse voltage is applied between themetal terminal 21 and the metal foil layer 12 of the lithium ion battery1 that is the subject of measurement via a connection terminal 35, andby the voltage measurement unit 32, a variation with time of a voltageheld in a capacitance of the lithium ion battery 1 is measured. To bemore specific, as shown in FIG. 4, the impulse voltage supplies apredetermined level of electric current to a coil 33, and then thesupply is halted, so that a predetermined voltage is induced in the coil33. This voltage acts as an impulse voltage, causing an electric currentI to be applied between the metal terminal 21 and the metal foil layer12 via a diode 34 and the connection terminal 35, and thus electriccharge is charged up in the capacitance C of the lithium ion battery 1.At this time, in a case where the lithium ion battery 1 is in a normalstate without an insulation failure, the maximum value of a hold voltagebeing charged up attains a given value (see the OK waveform shown inFIG. 6), whereas in a case where the lithium ion battery 1 has aninsulation failure, the hold voltage being charged up does not rise to adesired maximum value.

Furthermore, at timing T1 at which the hold voltage charged up in thelithium ion battery 1 in the normal state reaches a maximum value V1,the voltage measurement unit 32 reads a value of the hold voltage of thelithium ion battery 1, and at timing T2 after a lapse of a predeterminedtime from the timing T1, it again reads a value of the hold voltage. Inthis case, however, if there is no insulation failure, the hold voltageheld in the capacitance of the lithium ion battery 1 decreases slowly,whereas if there is an insulation failure, electric charge cannot beheld, and thus the hold voltage decreases abruptly (see the NG waveform2 shown in FIG. 6). As described above, the voltage measurement unit 32reads hold voltages V1 and V2 of the lithium ion battery 1 at the timingT1 at which the hold voltage reaches a maximum value and at the timingT2 after the lapse of a predetermined time therefrom, and thus, based onthe hold voltages V1 and V2 read at the timings T1 and T2, respectively,the lithium ion battery 1 can be evaluated for an insulation failure.

That is, in a case where the lithium ion battery 1 has an insulationfailure, the voltage V1 at the timing T1 does not rise to a value in thevicinity of a desired maximum value, or the voltage V2 at the timing T2drops significantly. The lithium ion battery 1 has an extremely smallcapacitance between the metal terminal 21 and the metal foil layer 12,and as shown in FIG. 3, the metal terminal 21 connected to theelectrolyte and to the battery cell is insulated from the metal foillayer 12 only by the heat-sealable resin layer 13. As a material of theheat-sealable resin layer 13, for example, polypropylene is usedfavorably, and the heat-sealable resin layer 13 has a thickness of 10 μmto 100 μm. Hence, there is a possibility that applying a high voltagebetween the metal terminal 21 and the metal foil layer 12 easily causesthe heat-sealable resin layer 13 to melt, leading to new occurrence ofan insulation failure. Thus, it is preferable to use a voltage of 10 Vor lower as a voltage to be applied. Also in a case where anacid-denatured polyolefin resin layer is interposed between the metalfoil layer 12 and the heat-sealable resin layer 13, it is preferable touse a voltage of 10 V or lower as a voltage to be applied.

Next, the following describes a modification example of themanufacturing process of a lithium ion battery of this embodiment. FIGS.7A to 7D are plan views schematically showing a manufacturing process ofa lithium ion battery according to this modification example. In themanufacturing process of the lithium ion battery 1 of this embodiment,first, as shown in FIG. 7A, a film is cut into an oversized piece thatis then press-molded to form an outer packaging body 10 having a marginregion 10 e. The outer packaging body 10 thus obtained is folded in two,and the lithium ion battery main body 20 is housed in the housing space10 a. Then, as shown in FIG. 7B, two sides of the outer packaging body10 in the folded state including the metal terminal holding portion 10 bare heat-sealed, and an opening portion is provided on the side of themargin region 10 e, after which the electrolyte is filled in the outerpackaging body 10. Next, as shown in FIG. 7C, while the margin region 10e is left unsealed on the outer peripheral side, the opening portion ofthe outer packaging body 10 is heat-sealed to form the heat-sealingportion 10 c so that the lithium ion battery main body 20 ishermetically sealed together with the electrolyte in the outer packagingbody 10. Next, with one connection terminal 35 of the insulation failureinspecting apparatus 30 made to bite into a portion of the metal foillayer 12 lying in the margin region 10 e and the other connectionterminal 35 connected to the metal terminal 21 (negative electrode), aninsulation failure inspection is performed, after which, as shown inFIG. 7D, the margin region 10 e is separated by cutting away the outerperipheral side of the outer packaging body 10 relative to theheat-sealing portion 10 c, and thus the lithium ion battery 1 iscompleted.

FIG. 8 is a sectional view of the lithium ion battery in the insulationfailure inspecting step shown in FIG. 7C. As shown in FIG. 8, althoughthe margin region 10 e is formed on the outer peripheral side relativeto the heat-sealing portion 10 c, the portion of the metal foil layer 12is in conduction with a portion of the metal foil layer 12 lying on theinner peripheral side relative to the heat-sealing portion 10 c, andthus an impulse voltage applied from the one connection terminal 35 inthe margin region 10 e is charged in a capacitance between the portionof the metal foil layer 12 lying on the inner peripheral side relativeto the heat-sealing portion 10 c and the metal terminal 21. Furthermore,the connection terminal 35 has holding portions 36 for holding a subjectof measurement in a sandwiching manner, and the holding portions 36 havea sharp-shaped portion 36 a that bites into the subject of measurementthrough a base layer 11 formed on the surface of the subject ofmeasurement. As described above, the connection terminal 35 holds theouter packaging body 10 in a sandwiching manner with the holdingportions 36, with the sharp-shaped portion 36 a made to bite into themetal foil layer 12, and thus connection between the connection terminal35 and the metal foil layer 12 can be established easily. At this time,the base layer 11 is partially damaged by the sharp-shaped portion 36 a,so that a flaw is generated on the surface of the outer packaging body10. This damage to the base layer 11, however, does not remain in thelithium ion battery 1 as a completed product since the margin region 10e is removed after the inspection. The connection terminal 35 is notlimited to the configuration in which two holding portions 36 are usedto hold the outer packaging body 10 in a sandwiching manner and may havea configuration in which only the holding portion 36 having thesharp-shaped portion 36 a is used and pressed against the outerpackaging body 10 so that the sharp-shaped portion 36 a is brought intoconduction with the metal foil layer 12.

Furthermore, the method for manufacturing a lithium ion battery is notlimited to the above-described manufacturing processes, and thefollowing process can also be adopted. That is, as shown in FIG. 9,first, the electrolyte is filled in the outer packaging body 10, afterwhich an opening portion provided on the outer peripheral side relativeto the margin region 10 e is heat-sealed. Then, an insulation failureinspecting step is performed, followed by formation (conditions for theformation: 60° C., 5 hours), after which the insulation failureinspecting step is performed again. Next, the heat-sealing portion 10 con the inner peripheral side relative to the margin region 10 e isheat-sealed, and the insulation failure inspecting step is performed,after which the margin region 10 c is separated, and thus the lithiumion battery 1 is completed. Furthermore, the heat-sealing portions 10 cand 10 d of the completed lithium ion battery 1 might be bent at a timethe lithium ion battery 1 is housed in a housing case, and, therefore,in view of a possibility of a crack occurring in the heat-sealable resinlayer 13 due to such bending of the heat-sealing portions 10 c and 10 d,an insulation failure inspection may be performed as a final step afterthe step of bending the heat-sealing portions 10 c and 10 d. Asdiscussed above, in each of the manufacturing processes of a lithium ionbattery, the insulation failure inspecting step can be performed aftereach one of steps that might lead to the occurrence of an insulationfailure, such as the heat-sealing steps or the step of bending theheat-sealing portions, is performed, and a manufacturing process of alithium ion battery in which an insulation failure inspecting step isperformed at least once falls within the technical field of the presentinvention. In the insulation failure inspecting step, it is preferablethat, after the electrolyte is filled in the outer packaging body, animpulse voltage of 10 V or lower be applied between the metal terminal21 and the metal foil layer 12, and it is preferable that, before theelectrolyte is filled in the outer packaging body, an impulse voltage of1000 V or lower be applied between the metal terminal 21 and the metalfoil layer 12. Furthermore, it is preferable that, in the insulationfailure inspecting step performed before the electrolyte is filled inthe outer packaging body, one connection terminal 35 be connected to aportion of the metal foil layer 12 lying over a region in which themetal terminal 21 is held in a sandwiched manner.

EXAMPLE

Next, the following specifically describes the action and effects of thepresent invention by way of an example. This example is to make anevaluation regarding an insulation failure that newly occurs when animpulse voltage is applied to a lithium ion battery.

[Manufacturing of Outer Packaging Body]

On the upper surface of aluminum foil (thickness: 40 μm) on which astretched nylon film (thickness: 25 μm) acting as a base layer is notlaminated, acid-denatured polypropylene (thickness: 20 μm) wasmelt-extruded, and polypropylene (thickness: 15 μm) was laminatedthereon, whereby an outer packaging body composed of the stretched nylonfilm, aluminum foil, acid-denatured polypropylene, and polypropylene wasobtained

Next, the above-described outer packaging body was cut into a sheetpiece having a size of 60 mm (MD direction (machine direction)) by 60 mm(TD direction (transverse direction)), which was then folded in two inthe MD direction, and opposed two sides of the folded sheet piece wereheat-sealed so that a pouch-type outer packaging body having an openingat one side thereof was formed. Then, a lithium ion battery main bodyincluding a cell was sealed therein so that a metal terminal extendedout to the outside from the open one side, after which an electrolytewas injected and the opening portion was hermetically sealed over awidth of 3 mm while the metal terminal was held in a sandwiched manner,and thus a lithium ion battery was manufactured. In this case,heat-sealing was performed under conditions of a surface pressure of 2.0MPa, a sealing temperature of 170° C., and a sealing time of 5.0seconds.

Next, an insulation failure inspection was performed in which 100samples of the above-described lithium ion battery were prepared, and avoltage of 10 V was applied as an impulse voltage between a negativeelectrode terminal and aluminum foil of each of the samples for 90milliseconds. Similarly, for each of cases of using, as an impulsevoltage, a voltage of 300 V and a voltage of 500 V, an insulationfailure inspection was performed with respect to 100 lithium ionbatteries as samples. After that, with respect to these 300 lithium ionbatteries that have undergone the insulation failure inspections, onceagain, another insulation failure inspection was performed by applying avoltage of 10 V as an impulse voltage. In this manner, an evaluation wasmade regarding a frequency of the occurrence of an insulation failure inthe insulation failure inspecting step that was performed first, andresults of the evaluation are shown in Table 1.

TABLE 1 Applied Voltage (V) Evaluation 10 V Good 300 V Fair 500 V Poor

As shown in Table 1, in the case of applying a voltage of 500 V, aninsulation failure was detected in 10% of the samples as a whole (Poor),and in the case of applying a voltage of 300 V, an insulation failurewas detected in 3% of the samples as a whole (Fair), whereas in the caseof applying a voltage of 10 V, no insulation failure was detected(Good). These results confirm that, by using a voltage of about 10 V asan impulse voltage to be applied in an insulation failure inspection,new occurrence of an insulation breakdown in the failure inspecting stepcan be prevented.

The present invention is not limited to the foregoing embodiments andmay be variously modified. Any embodiment obtained by appropriatelycombining the technical features disclosed in the different embodiments,respectively, is also encompassed within the technical scope of thepresent invention. For example, the method for manufacturing anelectrochemical cell, the insulation failure inspecting method, and theinsulation failure inspecting apparatus of each of the embodiments ofthe present invention may be applied to, in addition to a lithium ionbattery, an electrochemical cell in which an electrochemical cell mainbody such as a capacitor or an electric double layer capacitor is housedin an outer packaging body.

LIST OF REFERENCE SYMBOLS

-   -   1 lithium ion battery    -   10 outer packaging body    -   10 a housing space    -   10 b metal terminal holding portion    -   11 base layer    -   12 metal foil layer    -   13 heat-sealable resin layer    -   20 lithium ion battery main body    -   21 metal terminal    -   30 insulation failure inspecting apparatus    -   31 voltage generation unit    -   32 voltage measurement unit    -   33 coil    -   34 diode    -   35 connection terminal    -   36 holding portion    -   36 a sharp-shaped portion

1. A method for manufacturing an electrochemical cell in which anelectrochemical cell main body including a positive electrode composedof a positive electrode active material and a positive electrode currentcollector, a negative electrode composed of a negative electrode activematerial and a negative electrode current collector, and an electrolytefilled between the positive electrode and the negative electrode ishermetically housed in an outer packaging body formed by sequentiallylaminating at least a metal foil layer and a heat-sealable resin layerso that a tip end of a metal terminal that is connected to each of thepositive electrode and the negative electrode protrudes to an outside,the method comprising: an insulation failure inspecting step in which animpulse voltage is applied between the metal terminal and the metal foillayer, and a waveform of a voltage applied to a capacitance between themetal terminal and the metal foil layer is measured.
 2. The method formanufacturing an electrochemical cell according to claim 1, wherein theinsulation failure inspecting step is performed after the metal terminalis held in a sandwiched manner by the outer packaging body and a holdingportion where the metal terminal is held is heat-sealed and before theelectrolyte is filled in the outer packaging body.
 3. The method formanufacturing an electrochemical cell according to claim 1 or 2, whereinthe insulation failure inspecting step is performed after theelectrolyte is filled in the outer packaging body.
 4. The method formanufacturing an electrochemical cell according to any one of claims 1to 3, wherein the insulation failure inspecting step is performed bymeasuring a value of a hold voltage held by the capacitance between themetal terminal and the metal foil layer immediately after the voltageapplication is halted and a value of the hold voltage held by thecapacitance between the metal terminal and the metal foil layer after alapse of a predetermined time from the halt of the voltage application.5. The method for manufacturing an electrochemical cell according to anyone of claims 1 to 4, wherein a voltage of 10 V or lower is used as avoltage to be applied between the metal terminal and the metal foillayer.
 6. The method for manufacturing an electrochemical cell accordingto any one of claims 1 to 5, wherein in a heat-sealing step in which aperipheral edge portion of the outer packaging body is heat-sealed sothat the mutually opposed heat-sealable resin layers are bonded to eachother, a margin region not to be heat-sealed is left unsealed on anouter peripheral side relative to a heat-sealing region, and in theinsulation failure inspecting step, an impulse voltage is appliedbetween a portion of the metal foil layer lying in the margin region andthe metal terminal.
 7. An insulation failure inspecting apparatus,comprising: a voltage generation unit that applies an impulse voltage toa subject of measurement; and a voltage measurement unit that measures avariation with time of a voltage held by the subject of measurement. 8.The insulation failure inspecting apparatus according to claim 7,wherein the voltage generation unit applies a voltage of 10 V or lower.9. The insulation failure inspecting apparatus according to claim 8 or9, wherein a connection terminal that connects the insulation failureinspecting apparatus to a subject of measurement has a holding portionfor holding the subject of measurement in a sandwiching manner, and theholding portion has a sharp-shaped portion that bites into the subjectof measurement through a base layer formed on a surface of the subjectof measurement.
 10. An insulation failure inspecting method using theinsulation failure inspecting apparatus according to claim 8 or 9,comprising: with respect to an electrochemical cell in which anelectrochemical cell main body including a positive electrode composedof a positive electrode active material and a positive electrode currentcollector, a negative electrode composed of a negative electrode activematerial and a negative electrode current collector, and an electrolytefilled between the positive electrode and the negative electrode ishermetically housed in an outer packaging body formed by sequentiallylaminating at least a metal foil layer and a heat-sealable resin layerso that a tip end of a metal terminal that is connected to each of thepositive electrode and the negative electrode protrudes to an outside,applying an impulse voltage between the metal terminal and the metalfoil layer, and measuring a value of a hold voltage held by acapacitance between the metal terminal and the metal foil layerimmediately after the voltage application is halted and a value of thehold voltage held by the capacitance between the metal terminal and themetal foil layer after a lapse of a predetermined time from the halt ofthe voltage application.